Electrolyte precursor solution, electrode assembly, battery, and electronic apparatus

ABSTRACT

An electrolyte precursor solution includes a metallic compound containing elements constituting an electrolyte, a solvent capable of dissolving the metallic compound, and an anionic surfactant having a sulfate group (SO 4   2− ) bonded to a hydrophobic group R. By reacting such an electrolyte precursor solution with active material particles containing lithium, lithium sulfate derived from the anionic surfactant is interposed at the interface between the surface of the active material particle and the electrolyte so as to enhance the dissociation of lithium ions at the interface, and thus, an excellent ion conductivity can be realized.

BACKGROUND 1. Technical Field

The present invention relates to an electrolyte precursor solution, anelectrode assembly, a battery using the electrode assembly, and anelectronic apparatus including the battery.

2. Related Art

As a power supply for many electronic apparatuses such as portableinformation apparatuses, a lithium battery (including a primary batteryand a secondary battery) has been used. In the lithium battery, a liquidelectrolyte is adopted because a high ion conductivity is obtained,however, an advanced technique is required for safely sealing the liquidelectrolyte between the positive electrode and the negative electrode soas to prevent the leakage of the electrolyte. Therefore, a solidelectrolyte capable of achieving both a high energy density and safetyhas been attracting attention.

As such a solid electrolyte, for example, JP-T-2011-529243 (PatentDocument 1) discloses a silicon-containing lithium lanthanum titanatecomposite solid electrolyte material, in which amorphous Si or anamorphous Si compound exists at a grain boundary between crystal grainsof lithium lanthanum titanate represented by the chemical formula:Li_(3-x)La_(2/3-x)TiO₃ (0<x<0.16).

Further, in Patent Document 1, a method in which a raw material solutionof lithium lanthanum titanate and a silicon precursor solution are mixedand reacted with each other by heating, followed by drying, therebyobtaining a composite powder, and the composite powder is pressed intothe form of a sheet and then sintered at a high temperature between1100° C. and 1400° C. for 1 hour to 10 hours, whereby a composite solidelectrolyte material is obtained is described as a method for producinga silicon-containing lithium lanthanum titanate composite solidelectrolyte material. According to the composite solid electrolytematerial obtained in this manner, the grain boundary electricalconductivity is significantly improved by existence of amorphous Si oran amorphous Si compound at a grain boundary between crystal grains oflithium lanthanum titanate.

However, in the above-mentioned method for producing asilicon-containing lithium lanthanum titanate composite solidelectrolyte material of Patent Document 1, as described above, sinteringis performed at a high temperature between 1100° C. and 1400° C., andtherefore, there is a fear that lithium is evaporated and released fromthe composite powder during sintering, or a byproduct is generated, anda composite solid electrolyte material having a desired composition maynot be obtained. Therefore, when the sintering temperature is set to,for example, lower than 1000° C. for suppressing the release of lithiumor the generation of a byproduct, sintering is not sufficient at theinterface between the crystal grains of lithium lanthanum titanate, andthere is a problem that the grain boundary resistance increases and theion conductivity decreases.

SUMMARY

An advantage of some aspects of the invention is to solve at least partof the above-mentioned problems and the invention can be implemented asthe following forms or application examples.

Application Example

An electrolyte precursor solution according to this application exampleincludes a metallic compound containing elements constituting anelectrolyte, a solvent capable of dissolving the metallic compound, andan anionic surfactant having a sulfate group.

According to the electrolyte precursor solution of this applicationexample, an anionic surfactant having a sulfate group is contained, andtherefore, when active material particles to be used as an electrodematerial of a battery and the electrolyte precursor solution are broughtinto contact with each other and reacted with each other, a sulfategroup which is a hydrophilic group is bonded to the surface of theactive material particle. Therefore, by existence of a sulfate groupbetween the active material particle and the electrolyte (metalliccompound), the active material is easily dissociated as an ion, andthus, the ion conductivity between the active material particle and theelectrolyte can be improved. That is, an electrolyte precursor solutioncapable of forming an electrolyte having a high ion conductivity can beprovided.

In the electrolyte precursor solution according to the above-mentionedapplication example, it is preferred that the anionic surfactant iscontained at a concentration 5 times or more and 15 times or less thecritical micelle concentration in the solvent.

According to this configuration, a sulfate group is reliably made toexist between the active material particle and the electrolyte, andthus, the ion conductivity can be improved.

In the electrolyte precursor solution according to the above-mentionedapplication example, it is preferred that the anionic surfactantcontains lithium.

According to this configuration, the anionic surfactant containslithium, and therefore, the amount of lithium as the active material isincreased, and thus, the lithium ion conductivity can be furtherimproved.

In the electrolyte precursor solution according to the above-mentionedapplication example, it is preferred that the anionic surfactantcontains a hydrophobic group having 4 or more carbon atoms or afluorinated alkyl group to which a sulfate group and lithium are bonded.

According to this configuration, when the anionic surfactant contains ahydrophobic group having 4 or more carbon atoms or a fluorinated alkylgroup, it exhibits hydrophobicity, and therefore shows a function as asurfactant, and by aligning this anionic surfactant such that thesulfate group faces the surface of the active material particle, thewettability of the electrolyte precursor solution exhibitinghydrophobicity can be improved.

Application Example

A method for producing an electrode assembly according to thisapplication example includes a step of forming an active materialportion having voids inside using active material particles,impregnating the active material portion with the electrolyte precursorsolution according to the above-mentioned application example, followedby drying, and firing the active material portion impregnated with theelectrolyte precursor solution at a lower temperature than the meltingpoint of the active material particles.

According to this application example, an electrode assembly whose ionconductivity is improved by combining an active material portioncomposed of active material particles with an electrolyte andinterposing a sulfate group of an anionic surfactant between the surfaceof the active material particle and the electrolyte in the voids of theactive material portion can be produced. Therefore, even if thetemperature during firing is set lower than the melting point of theactive material particle, a desired ion conductivity can be ensured, andalso in the case where the active material is lithium, by performingfiring at a low temperature, the release of lithium or the generation ofa byproduct during firing is suppressed, and thus, an electrode assemblyhaving a desired composition can be produced.

In the method for producing an electrode assembly according to theabove-mentioned application example, it is preferred that theimpregnating of the active material portion with the electrolyteprecursor solution, followed by drying is repeatedly performed.

According to this method, the filling ratio of the electrolyte to thevoids of the active material portion is improved to decrease theinternal resistance, and therefore, an electrode assembly having animproved capacitance per unit volume, that is, an improved energydensity can be produced.

In the method for producing an electrode assembly according to theabove-mentioned application example, it is preferred that the metalliccompound of the electrolyte precursor solution contains elementsconstituting a crystalline first electrolyte portion and an amorphoussecond electrolyte portion after firing.

According to this method, an electrolyte obtained after firing includesa crystalline first electrolyte portion in which the direction of ionconduction is restricted and an amorphous second electrolyte portion inwhich the direction of ion conduction is hardly restricted, andtherefore, a higher ion conductivity can be realized as compared withthe case where only a crystalline first electrolyte portion is included.

In the method for producing an electrode assembly according to theabove-mentioned application example, it is preferred that the methodfurther includes melting a third electrolyte which has a lower meltingpoint than the first electrolyte portion and the second electrolyteportion and constitutes an amorphous third electrolyte portion aftercooling, and impregnating the active material portion with the thirdelectrolyte, followed by cooling.

According to this method, a third electrolyte portion is further formedin the voids of the active material portion, and therefore, an ionconduction pathway (ion conduction path) between the active materialparticle and the electrolyte is further increased, and thus, a higherion conductivity can be realized.

Application Example

An electrode assembly according to this application example includes anactive material portion including a plurality of active materialparticles and having voids inside, and an electrolyte including acrystalline first electrolyte portion and an amorphous secondelectrolyte portion, wherein each of the active material particle, thefirst electrolyte portion, and the second electrolyte portion containslithium, the electrolyte is contained in the voids of the activematerial portion, and lithium sulfate is interposed between the surfaceof the active material particle and the electrolyte in the voids.

According to this application example, the electrolyte includes acrystalline first electrolyte portion and an amorphous secondelectrolyte portion, and therefore, as compared with the case where theelectrolyte is constituted by only a crystalline first electrolyteportion, the conduction (transfer) of lithium ions between the firstelectrolyte portion and the second electrolyte portion is efficientlyperformed. In addition, since the electrolyte is contained in the voidsof the active material portion and lithium sulfate is interposed betweenthe surface of the active material particle and the electrolyte in thevoids, the dissociation of lithium ions on the surface of the activematerial particle is enhanced. That is, due to the improvement of theconcentration of lithium ions between the active material particle andthe electrolyte in addition to the improvement of the ion conductivitybetween the first electrolyte portion and the second electrolyteportion, an electrode assembly having an improved ion conductivity canbe provided.

In the electrode assembly according to the above-mentioned applicationexample, it is preferred that the first electrolyte portion is ametallic compound represented by the following formula (1) having agarnet-type crystal structure, and contains a metal A having a crystalradius of 78 pm or more, and the metal A is contained in the firstelectrolyte portion and the second electrolyte portion.Li_(7-x)La₃(Zr_(2-x)A_(x))O₁₂  (1)

In the formula (1), x satisfies the following formula: 0.05≤x≤0.6, andas the metal A, at least one metal is selected from Nb, Ta, and Sb.

According to this configuration, the metal A having a crystal radius of78 pm or more is partially substituted for the Zr site of the firstelectrolyte portion, and therefore, a concentration gradient associatedwith the metal A is generated between the first electrolyte portion andthe second electrolyte portion. That is, at an interface where the firstelectrolyte portion and the second electrolyte portion are in contactwith each other, the interface is hardly clear due to the concentrationgradient of the metal A. That is, lithium ion conduction between thefirst electrolyte portion and the second electrolyte portion becomeseasy, and thus, an electrode assembly in which an active materialportion and an electrolyte having a high ion conductivity are combinedcan be provided.

In the electrode assembly according to the above-mentioned applicationexample, it is preferred that the electrolyte includes an amorphousthird electrolyte portion having a lower melting point than the firstelectrolyte portion and the second electrolyte portion.

According to this configuration, the electrolyte including the thirdelectrolyte portion in addition to the first electrolyte portion and thesecond electrolyte portion is contained in the voids of the activematerial portion, and therefore, ion conduction paths are increased, andthus, an electrode assembly having a further improved ion conductivitycan be realized. In addition, the third electrolyte portion has a lowermelting point than the first electrolyte portion and the secondelectrolyte portion, and therefore, an electrolyte material constitutingthe third electrolyte portion can be melted and filled in the voids ofthe active material portion. That is, the composition of the firstelectrolyte portion or the second electrolyte portion can be preventedfrom changing due to heat when filling the third electrolyte portion inthe active material portion.

Application Example

A battery according to this application example includes the electrodeassembly according to the above-mentioned application example, a currentcollector provided so as to come into contact with the active materialparticles on one face side of the electrode assembly, and a negativeelectrode provided on the other face side of the electrode assembly.

According to this application example, the electrode assembly isconfigured such that the active material portion and the electrolyte arecombined and therefore has a high energy density and a high ionconductivity, and thus, a battery having an excellent charge-dischargecharacteristic and a high capacity can be provided.

In the battery according to the above-mentioned application example, itis preferred that the negative electrode is composed of metallic lithiumor an alloy containing lithium, and a lithium reduction resistant layeris provided between the other face of the electrode assembly and thenegative electrode.

According to this configuration, the negative electrode is constitutedby metallic lithium or an alloy containing lithium, and therefore, ascompared with the case where the negative electrode is constituted byanother active material, a lithium supply source is increased, and thus,a battery having a high capacity can be realized. Further, a lithiumreduction resistant layer is provided between the other face of theelectrode assembly and the negative electrode, and therefore, the growthof lithium dendrites on the negative electrode side due to charge anddischarge can be prevented by the lithium reduction resistant layer.That is, a short circuit between the electrode assembly which functionsas the positive electrode and the negative electrode caused by thegrowth of lithium dendrites can be prevented.

Application Example

An electronic apparatus according to this application example includesthe battery according to the above-mentioned application example.

According to this application example, the battery which has anexcellent charge-discharge characteristic and a high capacity isincluded, and therefore, an electronic apparatus which can withstandlong-term repeated use can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic perspective view showing a structure of a lithiumbattery of a first embodiment.

FIG. 2 is a schematic cross-sectional view showing a structure of thelithium battery of the first embodiment.

FIG. 3 is an enlarged view showing an active material portion, a firstelectrolyte portion, a second electrolyte portion, and a thirdelectrolyte portion in an electrode assembly of the first embodiment.

FIG. 4 is a flowchart showing a method for producing an electrodeassembly in a lithium battery of the first embodiment.

FIG. 5 is a schematic view showing a state of an anionic surfactantcontained in an electrolyte precursor solution.

FIG. 6 is a schematic view showing a step in the method for producing anelectrode assembly.

FIG. 7 is a schematic view showing a step in the method for producing anelectrode assembly.

FIG. 8 is a schematic view showing a step in the method for producing anelectrode assembly.

FIG. 9 is a schematic view showing a step in the method for producing anelectrode assembly.

FIG. 10 is a schematic view showing a step in the method for producingan electrode assembly.

FIG. 11 is a perspective view showing a structure of a wearableapparatus as an electronic apparatus of a second embodiment.

FIG. 12 is a schematic cross-sectional view showing a structure of alithium battery of a modification example.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments embodying the invention will be described withreference to the drawings. Note that the drawings to be used aredisplayed by being appropriately enlarged or reduced in size so thatportions to be described are in a recognizable state.

First Embodiment

Battery

First, a battery of this embodiment will be described with reference toFIGS. 1 to 3 by showing a lithium battery as an example. FIG. 1 is aschematic perspective view showing a structure of a lithium battery of afirst embodiment, FIG. 2 is a schematic cross-sectional view showing astructure of the lithium battery of the first embodiment, and FIG. 3 isan enlarged view showing an active material portion, a first electrolyteportion, a second electrolyte portion, and a third electrolyte portionin an electrode assembly of the first embodiment.

As shown in FIG. 1, a lithium battery 100 of this embodiment includes anelectrode assembly 10 which functions as a positive electrode, and anelectrolyte layer 24 and a negative electrode 30 which are sequentiallystacked on the electrode assembly 10. The lithium battery 100 furtherincludes a current collector 41 which comes into contact with theelectrode assembly 10, and a current collector 42 which comes intocontact with the negative electrode 30. Each of the electrode assembly10, the electrolyte layer 24, and the negative electrode 30 isconstituted by a solid phase containing lithium, and therefore, thelithium battery 100 is a solid secondary battery which can be chargedand discharged.

The lithium battery 100 of this embodiment has, for example, a circulardisk shape, and the contour size is, for example, ϕ10 mm and thethickness is, for example, about 0.3 mm. The lithium battery 100 issmall and thin and also is a solid secondary battery which can becharged and discharged, and therefore can be favorably used as a powersupply for a portable information terminal such as a smartphone. Thesize or the thickness of the lithium battery 100 is not limited to thisvalue as long as molding can be performed. In the case where the contoursize is ϕ10 mm as in this embodiment, the thickness is estimated to beabout 0.1 mm when it is thin from the viewpoint of shapability, and itis estimated to be about up to 1 mm when it is thick from the viewpointof the lithium ion conduction property of the electrolyte, and if it istoo thick, the utilization efficiency of the active material isdeteriorated. The shape of the lithium battery 100 is not limited to acircular disk shape and may be a polygonal disk shape. Hereinafter, therespective layers will be described in detail.

As shown in FIG. 2, the electrode assembly 10 which functions as apositive electrode includes an active material portion 11 composed of aplurality of active material particles 11 a and an electrolyte 20. Adetailed description of the structure of the electrode assembly 10 andthe production method thereof will be given later, however, by includingthe active material portion 11 formed by sintering in a state where theactive material particles 11 a are in contact with one another in theelectrode assembly 10, the electrode assembly 10 is in a state where anelectron conduction property is imparted. Further, the current collector41 is provided so as to come into contact with the plurality of activematerial particles 11 a. The electrolyte 20 includes a crystalline firstelectrolyte portion 21, an amorphous second electrolyte portion 22, andalso an amorphous third electrolyte portion 23. As the crystalline firstelectrolyte portion 21 and the amorphous second electrolyte portion 22,materials having a higher ion conductivity than the third electrolyteportion 23 are selected and used.

As the amorphous third electrolyte portion 23, a material having a lowermelting point than the materials constituting the active materialparticles 11 a, the first electrolyte portion 21, and the secondelectrolyte portion 22 is selected and used.

The electrolyte layer 24 provided between the electrode assembly 10 andthe negative electrode 30 is constituted using an ion conductiveelectrolyte without containing the active material particles 11 a. Suchan electrolyte layer 24 suppresses generation of lithium dendrites onthe negative electrode 30 side due to charge and discharge of thelithium battery 100, and functions as a lithium reduction resistantlayer which prevents an electrical short circuit between the electrodeassembly 10 to which an electron conduction property is imparted and thenegative electrode 30 due to lithium dendrites.

Hereinafter, a description will be given by referring to a face of theelectrode assembly 10 which comes into contact with the currentcollector 41 as “one face 10 c” and a face of the electrode assembly 10which comes into contact with the electrolyte layer 24 as “the otherface 10 a” in the lithium battery 100 of this embodiment.

Electrode Assembly

FIG. 3 is a view schematically showing a state where a sample obtainedby slicing the electrode assembly 10 thin is observed with atransmission electron microscope (TEM). As shown in FIG. 3, theelectrode assembly 10 includes the plurality of active materialparticles 11 a constituting the active material portion 11, and theelectrolyte 20 is filled between the particles of the active materialparticles 11 a. Each of the active material particle 11 a and the firstelectrolyte portion 21 of the electrolyte 20 is in the form of aparticle, and the particle diameter of the first electrolyte portion 21is much smaller than the particle diameter of the active materialparticle 11 a. The first electrolyte portion 21 exists between theparticles of the active material particles 11 a while being in contactwith the surface of the active material particle 11 a. Further, theamorphous second electrolyte portion 22 and the amorphous thirdelectrolyte portion 23 exist so as to fill the gap between the particlesof the active material particles 11 a and come into contact with theactive material particle 11 a and the first electrolyte portion 21. Itis preferred that all the gaps between the particles of the activematerial particles 11 a are filled with the electrolyte 20, however, infact, some gaps are in a state of including a space 11 s.

The interface between the active material particle 11 a and theelectrolyte 20, the interface of the third electrolyte portion 23 in theelectrolyte 20, and the interface of the space 11 s between theparticles of the active material particles 11 a are clear, however, theinterface between the first electrolyte portion 21 and the secondelectrolyte portion in the electrolyte 20 is not clear. In FIG. 3, forconvenience of illustration, the shape of the particle of each of theactive material particle 11 a and the first electrolyte portion 21 isshown in a spherical shape, however, the actual shape of the particle isnot necessarily a spherical shape, but is an indefinite shape.

From the viewpoint that an electron conduction property is exhibited bybringing the particles of the active material particles 11 a intocontact with one another, as for the particle diameter of the activematerial particle 11 a, for example, the average particle diameter D50thereof is preferably set to 500 nm or more and less than 10 μm. On theother hand, as for the particle diameter of the first electrolyteportion 21, for example, the average particle diameter D50 thereof is ata submicron level in relation to the below-mentioned production method.In FIG. 3, the particles of the first electrolyte portion 21 areillustrated in a recognizable state, however, in fact, fine particles ata submicron level come into contact with one another and form the firstelectrolyte portion 21.

As the active material particle 11 a which is a positive electrodeactive material constituting the active material portion 11, it ispreferred to use a lithium composite metal oxide which contains at leastLi, and further contains at least one type of transition metal selectedfrom V, Cr, Mn, Fe, Co, Ni, and Cu as the constituent element because itis chemically stable. Examples of such a lithium composite metal oxideinclude LiCoO₂, LiNiO₂, LiMn₂O₄, Li₂Mn₂O₃, Li(Ni_(x)Mn_(y)Co_(1-x-y))O₂[0<x+y<1], Li (Ni_(x)Co_(y)Al_(1-x-y))O₂ [0<x+y<1],LiCr_(0.5)Mn_(0.5)O₂, LiFePO₄, Li₂FeP₂O₇, LiMnPO₄, LiFeBO₃, Li₃V₂(PO₄)₃, Li₂CuO₂, Li₂FeSiO₄, and Li₂MnSiO₄. Further, solid solutions inwhich the atoms in a crystal of any of these lithium composite metaloxides are partially substituted with a typical metal, an alkali metal,an alkaline earth metal, a lanthanoid, a chalcogenide, a halogen, or thelike are also included in the lithium composite metal oxide, and any ofthese solid solutions can also be used as the active material particle11 a. In this embodiment, as the active material particle 11 a, a LiCoO₂particle is used, and hereinafter, the LiCoO₂ particle is sometimesreferred to as “LCO particle” for short.

As a method for forming the active material portion 11 including theplurality of active material particles 11 a, the active material portion11 may be formed into a thin film using a press sintering method, avapor phase deposition method such as CVD, PLD, sputtering, or aerosoldeposition other than a green sheet method. Further, a single crystalgrown from a melt or a solution may be used. In the case where a greensheet method or a press sintering method is used as the method forforming the active material portion 11, voids occur between theparticles of the active material particles 11 a after sintering. Suchvoids are in a state of communicating with one another inside the activematerial portion 11. When the voids are filled with the electrolyte 20,a contact area between the active material particle 11 a and theelectrolyte 20 increases, so that the interfacial impedance of theelectrode assembly 10 can be decreased. In consideration of theinterfacial impedance of the electrode assembly 10, the bulk densityporosity in the active material portion 11 is preferably from 40% to60%, and the filling ratio of the electrolyte 20 in the voids ispreferably 80% or more. The bulk density porosity a is derived from thefollowing formula (1) using the apparent volume v and the mass w of theactive material portion 11 and the density p of the active materialparticle 11 a.a={1−w/(v·ρ)}×100  (1)

The filling ratio of the electrolyte 20 can be determined by dividingthe value obtained by subtracting the mass before filling from the massafter filling by the density of the electrolyte 20.

The electrical resistivity of the active material portion 11 ispreferably 700 Ω·cm or less. When the active material portion 11 hassuch an electrical resistivity, a sufficient output can be obtained inthe lithium battery 100 using the electrode assembly 10. The electricalresistivity can be determined by adhering a copper foil to be used as anelectrode to the surface of the active material portion 11, andperforming DC polarization measurement.

Electrolyte

As the electrolyte 20 (the first electrolyte portion 21, the secondelectrolyte portion 22, and the third electrolyte portion 23) and theelectrolyte layer 24 included in the electrode assembly 10, acrystalline or amorphous material which is a solid electrolyte and iscomposed of a metallic compound such as an oxide, a sulfide, a halide, anitride, a hydride, or a boride can be used.

Example of the oxide crystalline material includeLi_(0.35)La_(0.55)TiO₃, Li_(0.2)La_(0.27)NbO₃, and a perovskite-typecrystal or a perovskite-like crystal in which the elements in a crystalthereof are partially substituted with N, F, Al, Sr, Sc, Nb, Ta, Sb, alanthanoid element, or the like, Li₇La₃Zr₂O₁₂, Li₅La₃Nb₂O₁₂,Li₅BaLa₂TaO₁₂, and a garnet-type crystal or a garnet-like crystal inwhich the elements in a crystal thereof are partially substituted withN, F, Al, Sr, Sc, Nb, Ta, Sb, a lanthanoid element, or the like,Li_(1.3)Ti_(1.7)Al_(0.3)(PO₄)₃, Li_(1.4)Al_(0.4)Ti_(1.6)(PO₄)₃,Li_(1.4)Al_(0.4)Ti_(1.4)Ge_(0.2) (PO₄)₃, and a NASICON-type crystal inwhich the elements in a crystal thereof are partially substituted withN, F, Al, Sr, Sc, Nb, Ta, Sb, a lanthanoid element, or the like, aLISICON-type crystal such as Li₁₄ZnGe₄O₁₆, and other crystallinematerials such as Li_(3.4)V_(0.6)Si_(0.4)O₄, Li_(3.6)V_(0.4)Ge_(0.6)O₄,and Li_(2+x)C_(1-x)B_(x)O₃.

Example of the sulfide crystalline material include Li₁₀GeP₂S₁₂,Li_(9.6)P₃S₁₂, Li_(9.54)Si_(1.74)P_(1.44)S_(11.7)Cl_(0.3), and Li₃PS₄.

Examples of other amorphous materials include Li₂O—TiO₂,La₂O₃—Li₂O—TiO₂, LiNbO₃, LiSO₄, Li₄SiO₄, Li₃PO₄—Li₄SiO₄, Li₄GeO₄—Li₃VO₄,Li₄SiO₄—Li₃VO₄, Li₄GeO₄—Zn₂GeO₂, Li₄SiO₄—LiMoO₄, Li₃PO₄—Li₄SiO₄,Li₄SiO₄—Li₄ZrO₄, SiO₂—P₂O₅—Li₂O, SiO₂—P₂O₅—LiCl, Li₂O—LiCl—B₂O₃,LiAlCl₄, LiAlF₄, LiF—Al₂O₃, LiBr—Al₂O₃, Li_(2.88)PO_(3.73)N_(0.14),Li₃N—LiCl, Li₆NBr₃, Li₂S—SiS₂, and Li₂S—SiS₂—P₂S₅.

Among the above-mentioned solid electrolytes, as the solid electrolyteto be used for the first electrolyte portion 21, a garnet-type crystalor a garnet-like crystal, which has an excellent ion conductivity, andin which the elements in a crystal of Li₇La₃Zr₂O₁₂ are partiallysubstituted with Al, Sr, Sc, Nb, Ta, Sb, a lanthanoid element, or thelike is preferred. Specific examples thereof include a compoundrepresented by the following formula (2).Li_(7-x)La₃(Zr_(2-x)A_(x))O₁₂  (2)

In the formula (2), x satisfies the following formula: 0.05×0.6, and themetal A has an atomic crystal radius of 78 pm or more, and at least onemetal is selected from Nb, Ta, and Sb. Hereinafter, the lithiumcomposite metal oxide represented by the above formula (2) is denotedfor short by “LLZrAO”. For example, the total ion conductivity ofLLZrNbO (x=0.3) is 1.6×10⁻⁴ [S/cm] (the grain bulk ion conductivity is6.2×10⁻⁴ [S/cm], and the grain boundary ion conductivity is 2.2×10⁻⁴[S/cm]).

According to the below-mentioned method for producing the electrodeassembly 10, the second electrolyte portion 22 is composed of anamorphous solid electrolyte containing the same metal A as that of thefirst electrolyte portion 21. Therefore, the metal A is partiallysubstituted for the Zr site in the crystal as shown in the above formula(2) in the first electrolyte portion 21, and also is contained in theamorphous second electrolyte portion 22, and therefore, a concentrationgradient associated with the metal A occurs between the firstelectrolyte portion 21 and the second electrolyte portion 22, and thus,the interface between the crystalline first electrolyte portion 21 andthe amorphous second electrolyte portion 22 is hardly clear. Lithiumions conduct in the crystalline material by hopping conduction in thecrystalline first electrolyte portion 21, and conduct in the amorphoussecond electrolyte portion 22 by ion diffusion. Therefore, by connectingthe crystalline first electrolyte portions 21 through the amorphoussecond electrolyte portion 22, lithium ions conduct by ion diffusionbetween the crystalline first electrolyte portions 21, and therefore, ascompared with the case where a grain boundary exists between thecrystalline first electrolyte portions 21, the ion conductivity in theelectrolyte 20 is improved.

As the third electrolyte portion 23, Li_(2+x)C_(1-x)B_(x)O₃ which is alithium composite oxide containing carbon (C) and boron (B), and hashigh coverage for the surface of the active material portion 11 (porousactive material sintered body) and the voids therein, and has a lowermelting point than the above-mentioned active material particles 11 a,the first electrolyte portion 21, and the second electrolyte portion 22,or an analogous substance thereof is particularly preferably used.Hereinafter, Li_(2+x)C_(1-x)B_(x)O₃ is denoted for short by “LCBO”.

Further, according to the below-mentioned method for producing theelectrode assembly 10, lithium sulfate exists between the surface of theactive material particle 11 a and the electrolyte 20. Lithium sulfate isderived from the anionic surfactant contained in the electrolyteprecursor solution to be used when forming the electrolyte 20. Lithiumsulfate present between the surface of the active material particle 11 aand the electrolyte 20 is as thin as a single molecular layer or so, andthe illustration thereof is omitted in FIG. 3. By interposing lithiumsulfate between the surface of the active material particle 11 a and theelectrolyte 20, the dissociation of lithium ions as an active materialis enhanced.

As a method for forming the electrolyte layer 24 using theabove-mentioned solid electrolyte, other than a solution process such asa so-called sol-gel method involving a hydrolysis reaction of anorganometallic compound or the like or an organometallic thermaldecomposition method, a CVD method using an appropriate metalliccompound in an appropriate gas atmosphere, an ALD method, a green sheetmethod or a screen printing method using a slurry of solid electrolyteparticles, an aerosol deposition method, a sputtering method using anappropriate target and an appropriate gas atmosphere, a PLD method, aflux method using a melt or a solution, or the like can be used. In thisembodiment, as a method for forming the electrolyte layer 24, asputtering method is used.

In this embodiment, the same solid electrolyte is used for the thirdelectrolyte portion 23 included in the electrode assembly 10 and theelectrolyte layer 24, however, different solid electrolytes may be used.

The electrode assembly 10 is subjected to a polishing treatment so thatthe plurality of active material particles 11 a are exposed on the oneface 10 c which comes into contact with the current collector 41. Byconnecting the current collector 41 to the plurality of active materialparticles 11 a exposed on the one face 10 c, the electrical resistancebetween the electrode assembly 10 and the current collector 41 isdecreased.

Negative Electrode

As a negative electrode active material which can be used as thenegative electrode 30 include Nb₂O₅, V₂O₅, TiO₂, In₂O₃, ZnO, SnO₂, NiO,ITO (indium tin oxide), AZO (Al-doped zinc oxide), FTO (F-doped tinoxide), an anatase phase of TiO₂, lithium composite metal oxides such asLi₄Ti₅O₁₂ and Li₂Ti₃O₇, metals such as Li, Si, Sn, Si—Mn, Si—Co, Si—Ni,In, and Au and alloys containing such metals, a carbon material, amaterial obtained by intercalation of lithium ions between layers of acarbon material, and the like can be exemplified. In consideration ofthe discharge capacity of the lithium battery 100 which is small andthin, the negative electrode 30 is preferably metallic Li or a metalsimple substance and an alloy which form a lithium alloy. The alloy isnot particularly limited as long as it can occlude and release lithium,but is preferably an alloy containing any of metals or metalloidelements in groups 13 and 14 excluding carbon, more preferably a metalsimple substance such as aluminum, silicon, or tin, or an alloy or acompound containing these atoms. These may be used alone or two or moretypes thereof may be used in any combination at any ratio. As the alloy,lithium alloys such as Li—Al, Li—Ni, Li—Si, Li—Sn, and Li—Sn—Ni, siliconalloys such as Si—Zn, tin alloys such as Sn—Mn, Sn—Co, Sn—Ni, Sn—Cu, andSn—La, Cu₂Sb, La₃Ni₂Sn₇, and the like can be exemplified.

As a method for forming the negative electrode 30 using theabove-mentioned negative electrode active material, other than asolution process such as a so-called sol-gel method involving ahydrolysis reaction of an organometallic compound or the like or anorganometallic thermal decomposition method, any method such as a CVDmethod using an appropriate metallic compound in an appropriate gasatmosphere, an ALD method, a green sheet method or a screen printingmethod using a slurry of a solid negative electrode active material, anaerosol deposition method, a sputtering method using an appropriatetarget and an appropriate gas atmosphere, a PLD method, a vacuumdeposition method, a plating method, or a thermal spraying method may beused.

Current Collector

As the current collectors 41 and 42, for example, one type of metal(metal simple substance) selected from the metal group consisting ofcopper (Cu), magnesium (Mg), titanium (Ti), iron (Fe), cobalt (Co),nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), indium (In), gold(Au), platinum (Pt), silver (Ag), and palladium (Pd), an alloy composedof two or more types of metals selected from this metal group, or thelike is used.

In this embodiment, as the current collectors 41 and 42, copper (Cu) isused. The thickness of each of the current collectors 41 and 42 is, forexample, from 20 μm to 40 μm. The lithium battery 100 does notnecessarily include a pair of current collectors 41 and 42 and mayinclude one of the current collectors 41 and 42. For example, in thecase where a plurality of lithium batteries 100 are stacked so as to beelectrically connected in series and used, a configuration in which thelithium battery 100 includes only the current collector 41 of the pairof current collectors 41 and 42 may be adopted.

Method for Producing Lithium Battery (Method for Producing ElectrodeAssembly)

A method for producing the lithium battery 100 of this embodiment ischaracterized by a method for producing the electrode assembly 10.Therefore, the method for producing the electrode assembly 10 will bedescribed with reference to FIGS. 4 to 10. FIG. 4 is a flowchart showingthe method for producing the electrode assembly in the lithium batteryof the first embodiment, and FIG. 5 is a schematic view showing a stateof an anionic surfactant contained in an electrolyte precursor solution.FIGS. 6 to 10 are each a schematic view showing a step in the method forproducing the electrode assembly.

As shown in FIG. 4, the method for producing the electrode assembly 10of this embodiment includes a step of preparing an electrolyte precursorsolution (step S1), a step of forming an active material portion 11(step S2), a step of impregnating the active material portion 11 withthe electrolyte precursor solution and performing drying (step S3), afiring step (step S4), a step of filling a third electrolyte (step S5),and a polishing step (step S6). Hereinafter, the respective steps willbe described sequentially.

In the step S1, first, various metal elements contained in the firstelectrolyte portion 21 and the second electrolyte portion 22 areobtained as metallic compounds, respectively, and each metallic compoundsolution in which the metallic compound is dissolved in a solvent isprepared. The metallic compounds to serve as objects in this embodimentare a lithium compound, a lanthanum compound, a zirconium compound, aniobium compound, a tantalum compound, and an antimony compound.

Examples of the lithium compound (lithium source) include lithium metalsalts such as lithium chloride, lithium nitrate, lithium acetate,lithium hydroxide, and lithium carbonate, and lithium alkoxides such aslithium methoxide, lithium ethoxide, lithium propoxide, lithiumisopropoxide, lithium butoxide, lithium isobutoxide, lithiumsec-butoxide, lithium tert-butoxide, and lithium dipivaloylmethanate,and among these, one type can be used or two or more types can be usedin combination.

Examples of the lanthanum compound (lanthanum source) include lanthanummetal salts such as lanthanum chloride, lanthanum nitrate, and lanthanumacetate, and lanthanum alkoxides such as lanthanum trimethoxide,lanthanum triethoxide, lanthanum tripropoxide, lanthanumtriisopropoxide, lanthanum tributoxide, lanthanum triisobutoxide,lanthanum tri-sec-butoxide, lanthanum tri-tert-butoxide, and lanthanumdipivaloylmethanate, and among these, one type can be used or two ormore types can be used in combination.

Examples of the zirconium compound (zirconium source) include zirconiummetal salts such as zirconium chloride, zirconium oxychloride, zirconiumoxynitrate, zirconium oxyacetate, and zirconium acetate, and zirconiumalkoxides such as zirconium tetramethoxide, zirconium tetraethoxide,zirconium tetrapropoxide, zirconium tetraisopropoxide, zirconiumtetrabutoxide, zirconium tetraisobutoxide, zirconium tetra-sec-butoxide,zirconium tetra-tert-butoxide, and zirconium dipivaloylmethanate, andamong these, one type can be used or two or more types can be used incombination.

Examples of the niobium compound (niobium source) as a compound havingan atomic crystal radius of 78 pm or more include niobium metal saltssuch as niobium chloride, niobium oxychloride, niobium oxalate, andniobium pentaacetylacetonate, and niobium alkoxides such as niobiumpentaethoxide, niobium pentapropoxide, niobium pentaisopropoxide, andniobium penta-sec-butoxide, and among these, one type can be used or twoor more types can be used in combination.

Similarly, examples of the tantalum compound (tantalum source) as acompound having an atomic crystal radius of 78 pm or more includetantalum metal salts such as tantalum chloride and tantalum bromide, andtantalum alkoxides such as tantalum pentamethoxide, tantalumpentaethoxide, tantalum pentaisopropoxide, tantalum penta-n-propoxide,tantalum pentaisobutoxide, tantalum penta-n-butoxide, tantalumpenta-sec-butoxide, and tantalum penta-tert-butoxide, and among these,one type can be used or two or more types can be used in combination.

Further, examples of the antimony compound (antimony source) as acompound having an atomic crystal radius of 78 pm or more includeantimony metal salts such as antimony bromide, antimony chloride, andantimony fluoride, and antimony alkoxides such as antimony trimethoxide,antimony triethoxide, antimony triisopropoxide, antimonytri-n-propoxide, antimony triisobutoxide, and antimony tri-n-butoxide,and among these, one type can be used or two or more types can be usedin combination.

As the solvent, a single solvent of water or an organic solvent or amixed solvent thereof capable of dissolving each of a lithium compound,a lanthanum compound, a zirconium compound, and a metallic compoundhaving anatomic crystal radius of 78 pm or more is used.

Such an organic solvent is not particularly limited, however, examplesthereof include alcohols such as methanol, ethanol, n-propyl alcohol,isopropyl alcohol, allyl alcohol, and 2-n-butoxyethanol, glycols such asethylene glycol, propylene glycol, butylene glycol, hexylene glycol,pentanediol, hexanediol, heptanediol, and dipropylene glycol, ketonessuch as acetone, methyl ethyl ketone, methyl propyl ketone, and methylisobutyl ketone, esters such as methyl formate, ethyl formate, methylacetate, and methyl acetoacetate, ethers such as diethylene glycolmonomethyl ether, diethylene glycol monoethyl ether, diethylene glycoldimethyl ether, ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, and dipropylene glycol monomethyl ether, organic acidssuch as formic acid, acetic acid, and propionic acid, and aromatics suchas toluene, o-xylene, and p-xylene.

As described above, the solvent is appropriately selected according tothe metallic compounds containing the metal elements constituting thefirst electrolyte portion 21 and the second electrolyte portion 22.Therefore, there is a possibility that not only water, but also anoil-based organic solvent is selected as the solvent, and also thesolvent is not limited to one type, but by combining a plurality oftypes of solvents, the solubility of the metallic compounds may beensured.

In the preparation of the metallic compound solution, each of theabove-mentioned metallic compounds is weighed at a concentration in theunit of mole (mol), and added to the selected solvent and dissolvedtherein by mixing. In order to sufficiently dissolve the metalliccompounds, mixing is performed by heating the solvent as needed.

Subsequently, in consideration of the composition of each of the firstelectrolyte portion 21 and the second electrolyte portion 22 to beobtained as a product, the metallic compound solutions in which themetallic compound is dissolved are weighed for each metal source andmixed, whereby an electrolyte precursor solution is obtained.Specifically, three types of metallic compound solutions containing alithium compound, a lanthanum compound, and a zirconium compound,respectively, a metallic compound solution containing at least one typeof metallic compound selected from a niobium compound, a tantalumcompound, and an antimony compound, and an anionic surfactant are mixedat a given mixing ratio.

The anionic surfactant is used for allowing lithium sulfate whichenhances the dissociation of lithium ions to exist between the activematerial particle 11 a and the electrolyte 20 (in this case, the firstelectrolyte portion 21 and the second electrolyte portion 22) asdescribed above, and preferably contains lithium which is an activematerial. Further, the anionic surfactant contains a hydrophobic group Rto which a sulfate group (SO₄ ²⁻) which is a hydrophilic group andlithium (Li) are bonded, and the hydrophobic group R preferably has 4 ormore carbon atoms or is preferably a fluorinated alkyl group. When thehydrophobic group R has 4 or more carbon atoms or is a fluorinated alkylgroup, the hydrophobicity is improved, and the function as a surfactantis exhibited, and also the range of selection of the above-mentionedsolvent can be expanded on the oil-based side. Therefore, the anionicsurfactant is represented by the following formula (3).R—SO₄—Li  (3)

Specific examples of the hydrophobic group R having 4 or more carbonatoms include linear alkyl groups such as an n-butyl group, an n-pentylgroup, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonylgroup, an n-decyl group, an n-undecyl group, an n-dodecyl group, ann-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, ann-hexadecyl group, an n-heptadecyl group, and an n-octadecyl group,branched alkyl groups such as a sec-butyl group, a tert-butyl group, aniso-amyl group, a tert-amyl group, and a 2-ethylhexyl group, andfluorinated alkyl groups such as a 2-fluoroethyl group and a2,2,2-trifluoroethyl group.

In this embodiment, lithium dodecyl sulfate (LDS) in which a sulfategroup (SO₄ ²⁻) and lithium (Li) are bonded to the hydrophobic group Rwhich is an alkyl group having 12 carbon atoms is used as the anionicsurfactant.

As shown in FIG. 5, when an anionic surfactant 25 is mixed with, forexample, an aqueous solvent, a micelle 25 m in which a plurality ofmolecules of the anionic surfactant 25 gather with the sulfate group(SO₄ ²⁻) facing outward and the hydrophobic group R facing inward isformed in the solvent. In the case where the anionic surfactant 25 ismixed with an oil-based solvent, a micelle 25 m in which a plurality ofmolecules of the anionic surfactant 25 gather with the hydrophobic groupR facing outward and the sulfate group (SO₄ ²⁻) facing inward is formed.The concentration of the anionic surfactant 25 at which the micelle 25 mis formed in the solvent in this manner is called “critical micelleconcentration (CMC)”. The critical micelle concentration (CMC) oflithium dodecyl sulfate (LDS) as the anionic surfactant 25 is 3.0 mmol(millimoles)/kg (solution).

The content of the anionic surfactant 25 in the electrolyte precursorsolution is preferably such that the anionic surfactant 25 is in a stateof being dispersed to some extent in the solution from the viewpointthat the effect of the anionic surfactant 25 is reliably brought about.In this embodiment, the content of the anionic surfactant 25 withrespect to the total amount of the solution is set to 5 times or moreand 15 times or less the critical micelle concentration. When thecontent of the anionic surfactant 25 in the solution exceeds 15 timesthe critical micelle concentration, most of the anionic surfactant 25 ismicellized in the solution, and the amount of the anionic surfactant 25to be dispersed in the solution is decreased. Then, the process proceedsto the step S2.

In the step S2, a porous active material portion 11 is formed.Specifically, first, a positive electrode active material ingredient(lithium composite metal oxide) in the form of particles (powder) isprepared. In this embodiment, LiCoO₂ (hereinafter referred to as “LCO”for short) in the form of particles is used as the positive electrodeactive material ingredient. The average particle diameter (D50) of thepositive electrode active material ingredient is, for example,preferably 300 nm or more and 20 μm or less, more preferably 5 μm ormore and 15 μm or less. The average particle diameter is measured, forexample, using a light scattering particle size distribution analyzer(for example, Nanotrac UPA-EX250, manufactured by Nikkiso Co., Ltd.)after dispersing the LCO particles in n-octanol at a concentration of0.1 mass % to 10 mass %. When the average particle diameter is toosmall, the voids become smaller, and it becomes difficult to fill thevoids with the electrolyte in the subsequent step. On the other hand,when the average particle diameter is too large, the specific surfacearea of the active material portion 11 becomes smaller, and the outputof the lithium battery 100 is decreased.

Subsequently, as shown in FIG. 6, a powder 11 p of the positiveelectrode active material ingredient is placed in a die (mold) 81 andcompression-molded by pressing at a pressure of, for example, 0.1 MPa to5.0 MPa using a pressing portion 82. Further, this compressed body issintered by a heat treatment, whereby the active material portion 11 isobtained. This heat treatment is performed under a temperature conditionwhich is 850° C. or higher and lower than the temperature which is thelower of either the melting point or the decomposition point of thelithium composite metal oxide to be used as the positive electrodeactive material ingredient in consideration of the evaporation oflithium. The melting point of LCO as the lithium composite metal oxideis higher than 1000° C., and therefore, this heat treatment ispreferably performed at 900° C. or higher and 1000° C. or lower.Further, this heat treatment is preferably performed for 5 minutes ormore and 36 hours or less, more preferably performed for 4 hours or moreand 14 hours or less.

To the positive electrode active material ingredient, a polymer compoundwhich functions as a binder may be added. Examples of such a polymercompound include polyvinylidene fluoride (PVdF), polyvinyl alcohol(PVA), and polypropylene carbonate (PPC). Such a polymer compound isburned or oxidized in the heat treatment in this step, and the amountthereof is reduced or the compound is destroyed by burning.

Further, to the positive electrode active material ingredient, a poreforming material may be added. The pore forming material refers to amaterial (for example, a polymer compound or a carbon powder) to serveas the template of a void. By adding the pore forming material, the bulkdensity porosity of the active material portion 11 can be controlled.The pore forming material is burned or oxidized in the heat treatment inthis step, and the amount thereof is reduced. The average particlediameter of the pore forming material is preferably from 0.5 μm to 10μm. The pore forming material may contain particles composed of adeliquescent material. Water formed around the particles bydeliquescence of the particles functions as a binder for binding thelithium composite metal oxide in the form of particles. Therefore, theshape of the compressed body can be maintained from when the positiveelectrode active material ingredient in the form of particles iscompression-molded until when the heat treatment is performed.

The method for forming the porous active material portion 11 having abulk density porosity of 40% to 60% is not limited to a press-sinteringmethod, and for example, a green sheet method may be used. Specifically,an LCO powder in which the average particle diameter D50 of the particlesize distribution is about 5 μm is mixed with 1,4-dioxane as the solventin which PPC as the binder (binding agent) is dissolved to form aslurry, and the slurry is applied to a polyethylene terephthalate (PET)film substrate using an automatic film applicator (manufactured by CotecCorporation), whereby a sheet is formed.

The composition of the slurry at this time can take an arbitrary valuein accordance with the thickness of a desired sheet or the performanceof the applicator. Further, to the slurry, an auxiliary agent such as adispersant, a defoaming agent, or a pore forming material may be addedas needed.

The thus formed sheet is punched with an appropriate punch, whereby apellet formed into a circular disk shape with a diameter of, forexample, about 10 mm is obtained. This pellet is degreased at about 300°C., and thereafter placed on a substrate composed of, for example,magnesium oxide and fired using, for example, an electric mufflefurnace. The firing temperature is 850° C. or higher and is preferably atemperature of 875° C. or higher and 1000° C. or lower, which is lowerthan the melting point of LCO serving as the positive electrode activematerial ingredient. The firing time is preferably set to, for example,5 minutes or more and 36 hours or less, and is more preferably 4 hoursor more and 14 hours or less.

According to this, the LCO particles are sintered to one another, andthus, the active material portion 11 which is a porous sintered bodyhaving voids (internal cavities) inside is obtained. Then, the processproceeds to the step S3.

In the step S3, the porous active material portion 11 is impregnatedwith the electrolyte precursor solution prepared in the step S1 anddried. Specifically, as shown in FIG. 7, the shaped active materialportion 11 is placed on a hot plate 85 through a substrate 84. Thesubstrate 84 is composed of, for example, magnesium oxide or the likewhich is heat resistant and prevents the active material portion 11 fromcoming into direct contact with the hot plate 85 so as to suppressdeterioration of the active material portion 11 by heating when heatingis performed with the hot plate 85.

A predetermined amount of the electrolyte precursor solution 60 isdropped from a nozzle 51 onto the active material portion 11 placed onthe substrate 84 using, for example, a constant amount discharger. Sincethe active material portion 11 is a porous material, the droppedelectrolyte precursor solution 60 permeates the active material portion11 by capillary phenomenon. In the case where the electrolyte precursorsolution 60 remains on the surface of the active material portion 11after a predetermined amount of the electrolyte precursor solution 60 isdropped, this solution is removed by wiping with a non-woven fabric orthe like. The electrolyte precursor solution 60 contains the anionicsurfactant 25, and therefore, the wettability of the electrolyteprecursor solution 60 on the active material portion 11 is improved, andthe electrolyte precursor solution 60 can be efficiently filled in thevoids inside the active material portion 11. Then, the solvent is driedby setting the temperature of the hot plate 85 to a temperature, whichis lower than 100° C. and at which the solvent can be evaporated. Theset temperature and the drying time depend on the type of the solvent,however, after the active material portion 11 reaches the settemperature, drying is performed for about 15 minutes. Subsequently, thetemperature of the hot plate 85 is set to, for example, 360° C., andheating is performed for 10 minutes, whereby hydrocarbons contained inthe electrolyte precursor solution 60 are burned and decomposed.Further, heating is performed for 10 minutes by setting the temperatureof the hot plate 85 to, for example, 540° C. which is lower than thesintering temperature of the active material portion 11, whereby theactive material portion 11 is calcined. Then, the active materialportion 11 is gradually cooled until the temperature thereof isdecreased to 50° C. or lower. According to this, the active materialportion 11 is impregnated with the electrolyte precursor solution 60,followed by drying and calcination, whereby various types of metalliccompounds contained in the electrolyte precursor solution 60 and theanionic surfactant 25 are deposited in the voids inside the activematerial portion 11.

By measuring the mass before and after the procedure of impregnation ofthe active material portion 11 with the electrolyte precursor solution60, and drying and calcination, the filling ratio of the electrolyte inthe voids of the active material portion 11 is determined. Based on thedetermined filling ratio of the electrolyte, the step S3 is repeateduntil the filling ratio reaches the desired state (for example, 70% ormore). Then, the process proceeds to the step S4.

In the step S4, the active material portion 11 after completion ofimpregnation with the electrolyte precursor solution 60, and drying andcalcination is fired (main firing). Specifically, a calcined body of theactive material portion 11 is placed in a pot which is heat resistantand is composed of, for example, magnesium oxide or the like, and thepot is covered with a lid. Then, the pot is placed in, for example, anelectric muffle furnace, and firing is performed for, for example, 8hours at a temperature from 900° C. to 1000° C. or lower, which is lowerthan the melting point of LCO particles (that is, the active materialparticles 11 a) constituting the active material portion 11 and higherthan the calcination temperature. According to this, various types ofmetallic compounds filled in the voids in the calcined body of theactive material portion 11 are subjected to a heat treatment, whereby acrystalline first electrolyte portion 21 and an amorphous secondelectrolyte portion 22 are formed. Further, as shown in FIG. 8, theanionic surfactant 25 (lithium dodecyl sulfate) adhered to the surfaceof the active material particle 11 a is thermally decomposed to removethe hydrophobic group R, whereby lithium sulfate is formed on thesurface of the active material particle 11 a. That is, the activematerial portion 11 is brought to a state where lithium sulfate existsbetween the active material particle 11 a and the electrolyte (the firstelectrolyte portion 21 and the second electrolyte portion 22) in thevoids of the active material portion 11. In this embodiment, a body in astate where the active material portion 11 and the electrolyte (thefirst electrolyte portion 21 and the second electrolyte portion 22) arecombined after the main firing is completed is called “main fired bodylop”. Then, the process proceeds to the step S5.

In the step S5, a third electrolyte is further filled in the voids ofthe main fired body 10 p. Specifically, as shown in FIG. 9, first, themain fired body 10 p is placed in a pot 91. The main fired body 10 p issupported by a support needle 92 provided on the bottom face of the pot91. The pot 91 is composed of, for example, magnesium oxide, and thesupport needle 92 is composed of, for example, gold (Au). On the mainfired body 10 p, a third electrolyte 23 p in a solid form is placed. Inthis embodiment, a face of the main fired body 10 p supported by thesupport needle 92 is to become the other face 10 a of the electrodeassembly 10 described above. On the other hand, a face of the main firedbody 10 p on which the third electrolyte 23 p is placed is referred toas “one face 10 b”.

In this embodiment, as the third electrolyte 23 p, LCBO(Li_(2+x)C_(1-x)B_(x)O₃) having a lower melting point than LLZrAOconstituting the first electrolyte portion 21 is used. The melting pointof LCBO is about 700° C., and therefore, the pot 91 is heated to about800° C. in an atmosphere containing carbon dioxide (CO₂) gas to melt thethird electrolyte 23 p placed on the main fired body 10 p, whereby amelt 23 m is obtained. The melt 23 m is impregnated into the main firedbody 10 p which is a porous material by capillary phenomenon.Thereafter, the pot 91 is rapidly cooled to room temperature, wherebythe impregnated melt 23 m is solidified. The melt 23 m of the thirdelectrolyte 23 p is further filled in the voids remaining between theparticles of the sintered active material particles 11 a inside the mainfired body 10 p and becomes the third electrolyte portion 23 aftercooling. By adjusting the amount of the melt 23 m, the surface of themain fired body 10 p is also covered with the third electrolyte portion23. By doing this, the electrode assembly 10 in which the electrolyte 20(the first electrolyte portion 21, the second electrolyte portion 22,and the third electrolyte portion 23) is filled in the porous main firedbody 10 p is completed. The average thickness of the electrode assembly10 at this time is, for example, about 110 μm. Then, the processproceeds to the step S6. The ion conductivity of LCBO is about 8.0×10⁻⁷[S/cm] and is lower than that of the first electrolyte portion 21.

In the step S6, as shown in FIG. 10, the one face 10 b of the electrodeassembly 10 in which the electrolyte 20 is filled is polished, wherebythe active material particles 11 a are exposed. The face on which theactive material particles 11 a are exposed is a polished face andcorresponds to the one face 10 c of the electrode assembly 10 shown inFIG. 2. Examples of a method for polishing the one face 10 b of theelectrode assembly 10 in this manner include a chemical mechanicalpolishing treatment (CMP treatment). In the case where the plurality ofactive material particles 11 a are sufficiently exposed on the one face10 b after filling the melt 23 m of the third electrolyte 23 p in themain fired body 10 p in the step S5, the polishing treatment is notnecessarily performed. That is, the step S6 may be omitted.

Thereafter, an electrolyte layer 24 is formed on the other face 10 a ofthe electrode assembly 10. In this embodiment, the electrolyte layer 24is formed by depositing LCBO which is the same material as that of thethird electrolyte portion 23 using a sputtering method. The thickness ofthe electrolyte layer 24 may be 1.5 μm or more and 100 μm or less, andis set to 2.5 μm in this embodiment.

Subsequently, a negative electrode 30 is stacked and formed on theelectrolyte layer 24. In this embodiment, the negative electrode 30 isformed by depositing metallic lithium using a sputtering method. Thethickness of the negative electrode 30 may be within a range of 50 nm ormore and 100 μm or less, and is set to about 15 μm in consideration ofthe discharge capacity in this embodiment.

Subsequently, as shown in FIG. 2, a current collector 41 is formed so asto come into contact with the one face 10 c of the electrode assembly10, and a current collector 42 is formed so as to come into contact withthe negative electrode 30. In this embodiment, the current collectors 41and 42 are formed by adhering a copper foil having a thickness of about20 μm, followed by press-bonding. By doing this, the lithium battery 100is completed.

Next, effects when electrolyte precursor solutions of Examples are usedwill be described by showing more specific Examples and ComparativeExamples of the electrolyte precursor solution to be used for formingthe electrode assembly 10.

EXAMPLE 1

The electrolyte precursor solution of Example 1 is an electrolyteprecursor solution in which the metallic compound constituting thecrystalline first electrolyte portion 21 is represented byLi_(6.7)La₃Zr_(1.7)Nb_(0.3)O₁₂ (LLZrNbO) and contains lithium dodecylsulfate (LDS) as an anionic surfactant at a concentration 5 times thecritical micelle concentration (CMC). Hereinafter, the preparation ofmetallic compound solutions to be used and the preparation of theelectrolyte precursor solution will be described.

Preparation of 1 mol/kg Lithium Compound Solution

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 0.6895 g of lithium nitrate 3N5 (manufactured by Kanto ChemicalCo., Inc.) as a lithium source and 9.3105 g of 2-n-butoxyethanol(manufactured by Kanto Chemical Co., Inc.) as a solvent are weighed, andthe bottle is placed on a hot plate with a stirrer function at a stirrerrotation speed of 300 rpm with an adjusted temperature of 170° C.Heating and stirring are performed for 30 minutes until lithium nitrateis completely dissolved. Thereafter, the resulting solution is graduallycooled to room temperature and used as a 1 mol/kg lithiumnitrate/2-n-butoxyethanol solution.

Preparation of 1 mol/kg Lanthanum Compound Solution

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 4.3301 g of lanthanum nitrate hexahydrate 4N (manufactured by KantoChemical Co., Inc.) as a lanthanum source and 5.6699 g of2-n-butoxyethanol (manufactured by Kanto Chemical Co., Inc.) as asolvent are weighed, and the bottle is placed on a hot plate with astirrer function at a stirrer rotation speed of 300 rpm with an adjustedtemperature of 140° C. Heating and stirring are performed for 30 minutesuntil lanthanum nitrate hexahydrate is completely dissolved. Thereafter,the resulting solution is gradually cooled to room temperature and usedas a 1 mol/kg lanthanum nitrate hexahydrate/2-n-butoxyethanol solution.

Preparation of 1 mol/kg Zirconium Compound Solution

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 4.7960 g of an 80 mass % butanol solution of zirconiumtetrabutoxide (manufactured by Gelest, Inc.) as a zirconium source and5.2040 g of 2-n-butoxyethanol (manufactured by Kanto Chemical Co., Inc.)as a solvent are weighed, and the bottle is placed on a stirrer at astirrer rotation speed of 300 rpm. Stirring is performed for 10 minutesuntil the 80 mass % butanol solution of zirconium tetrabutoxide and2-n-butoxyethanol are completely mixed. After completion of stirring,the resulting solution is used as a 1 mol/kg zirconiumtetrabutoxide/2-n-butoxyethanol solution.

Preparation of 1 mol/kg Niobium Compound Solution

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 3.1821 g of niobium pentaethoxide (manufactured by Kojundo ChemicalLab. Co., Ltd.) as a niobium source and 6.8179 g of 2-n-butoxyethanol(manufactured by Kanto Chemical Co., Inc.) as a solvent are weighed, andthe bottle is placed on a stirrer at a stirrer rotation speed of 300rpm. Stirring is performed for 10 minutes until niobium pentaethoxideand 2-n-butoxyethanol are completely mixed. After completion ofstirring, the resulting solution is used as a 1 mol/kg niobiumpentaethoxide/2-n-butoxyethanol solution.

Preparation of 15 mmol/kg Anionic Surfactant Solution (5 times CMC)

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 0.0409 g of lithium dodecyl sulfate (LDS) (manufactured by AcrosOrganics Co., Ltd.) as an anionic surfactant and 9.9591 g of ethanol asa solvent are weighed, and the bottle is placed on a hot plate with astirrer function at a stirrer rotation speed of 300 rpm with an adjustedtemperature of 165° C. Heating and stirring are performed for 30 minutesuntil LDS is completely dissolved. Thereafter, the resulting solution isgradually cooled to room temperature and used as a 15 mmol/kgLDS/ethanol solution.

Preparation of LLZrNbO Precursor Solution

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 8.0400 g of the 1 mol/kg lithium nitrate/2-n-butoxyethanolsolution, 3.0000 g of the 1 mol/kg lanthanum nitratehexahydrate/2-n-butoxyethanol solution, 1.7000 g of the 1 mol/kgzirconium tetrabutoxide/2-n-butoxyethanol solution, 0.3000 g of the 1mol/kg niobium pentaethoxide/2-n-butoxyethanol solution, and 1.0000 g ofthe 15 mmol/kg LDS/ethanol solution are weighed, and the bottle isplaced on a stirrer at a stirrer rotation speed of 300 rpm.

Stirring is performed for 10 minutes until the mixture is completelymixed. After completion of stirring, the resulting solution is used as a1 mol/kg Li_(6.7)La₃Zr_(1.7)Nb_(0.3)O₁₂ precursor (+LDS at aconcentration 5 times the CMC) solution.

EXAMPLE 2

The electrolyte precursor solution of Example 2 has the sameconfiguration as that of Example 1 except that the concentration of LDSas the anionic surfactant in Example 1 is changed to 15 times the CMC.That is, with respect to a lithium source (lithium nitrate), a lanthanumsource (lanthanum nitrate hexahydrate), a zirconium source (zirconiumtetrabutoxide), and a niobium source (niobium pentaethoxide), 1 mol/kgsolutions are prepared, respectively, in the same manner as in Example1.

Preparation of 45 mmol/kg Anionic Surfactant Solution (15 Times CMC)

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 0.1225 g of LDS as an anionic surfactant and 9.8775 g of ethanol asa solvent are weighed, and the bottle is placed on a hot plate with astirrer function at a stirrer rotation speed of 300 rpm with an adjustedtemperature of 165° C. Heating and stirring are performed for 30 minutesuntil LDS is completely dissolved. Thereafter, the resulting solution isgradually cooled to room temperature and used as a 45 mmol/kgLDS/ethanol solution.

Preparation of LLZrNbO Precursor Solution

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 8.0400 g of the 1 mol/kg lithium nitrate/2-n-butoxyethanolsolution, 3.0000 g of the 1 mol/kg lanthanum nitratehexahydrate/2-n-butoxyethanol solution, 1.7000 g of the 1 mol/kgzirconium tetrabutoxide/2-n-butoxyethanol solution, 0.3000 g of the 1mol/kg niobium pentaethoxide/2-n-butoxyethanol solution, and 1.0000 g ofthe 45 mmol/kg LDS/ethanol solution are weighed, and the bottle isplaced on a stirrer at a stirrer rotation speed of 300 rpm. Stirring isperformed for 10 minutes until the mixture is completely mixed. Aftercompletion of stirring, the resulting solution is used as a 1 mol/kgLi_(6.7)La₃Zr_(1.7)Nb_(0.3)O₁₂ precursor (+LDS at a concentration 15times the CMC) solution.

EXAMPLE 3

The electrolyte precursor solution of Example 3 is an electrolyteprecursor solution in which the metallic compound constituting thecrystalline first electrolyte portion 21 is represented byLi_(6.2)La₃Zr_(1.2)Sb_(0.4)Ta_(0.4)O₁₂ (LLZrSbTaO) and contains LDS asan anionic surfactant at a concentration 10 times the critical micelleconcentration (CMC). Hereinafter, the preparation of metallic compoundsolutions to be used and the preparation of the electrolyte precursorsolution will be described.

With respect to a lithium source (lithium nitrate), a lanthanum source(lanthanum nitrate hexahydrate), and a zirconium source (zirconiumtetrabutoxide), 1 mol/kg solutions are prepared, respectively, in thesame manner as in Example 1.

Preparation of 1 mol/kg Antimony Compound Solution

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 2.5694 g of antimony triethoxide (manufactured by Kojundo ChemicalLab. Co., Ltd.) as an antimony source and 7.4306 g of 2-n-butoxyethanol(manufactured by Kanto Chemical Co., Inc.) as a solvent are weighed, andthe bottle is placed on a stirrer at a stirrer rotation speed of 300rpm. Stirring is performed for 10 minutes until antimony triethoxide and2-n-butoxyethanol are completely mixed. After completion of stirring,the resulting solution is used as a 1 mol/kg antimonytriethoxide/2-n-butoxyethanol solution.

Preparation of 1 mol/kg Tantalum Compound Solution

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 4.0625 g of tantalum pentaethoxide (manufactured by KojundoChemical Lab. Co., Ltd.) as a tantalum source and 5.9375 g of2-n-butoxyethanol (manufactured by Kanto Chemical Co., Inc.) as asolvent are weighed, and the bottle is placed on a stirrer at a stirrerrotation speed of 300 rpm. Stirring is performed for 10 minutes untiltantalum pentaethoxide and 2-n-butoxyethanol are completely mixed. Aftercompletion of stirring, the resulting solution is used as a 1 mol/kgtantalum pentaethoxide/2-n-butoxyethanol solution.

Preparation of 30 mmol/kg Anionic Surfactant Solution (10 Times CMC)

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 0.0817 g of LDS as an anionic surfactant and 9.9183 g of ethanol asa solvent are weighed, and the bottle is placed on a hot plate with astirrer function at a stirrer rotation speed of 300 rpm with an adjustedtemperature of 165° C. Heating and stirring are performed for 30 minutesuntil LDS is completely dissolved. Thereafter, the resulting solution isgradually cooled to room temperature and used as a 30 mmol/kgLDS/ethanol solution.

Preparation of LLZrSbTaO Precursor Solution

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 7.4400 g of the 1 mol/kg lithium nitrate/2-n-butoxyethanolsolution, 3.0000 g of the 1 mol/kg lanthanum nitratehexahydrate/2-n-butoxyethanol solution, 1.2000 g of the 1 mol/kgzirconium tetrabutoxide/2-n-butoxyethanol solution, 0.4000 g of the 1mol/kg antimony triethoxide/2-n-butoxyethanol solution, 0.4000 g of the1 mol/kg tantalum pentaethoxide/2-n-butoxyethanol solution, and 1.0000 gof the 30 mmol/kg LDS/ethanol solution are weighed, and the bottle isplaced on a stirrer at a stirrer rotation speed of 300 rpm. Stirring isperformed for 10 minutes until the mixture is completely mixed. Aftercompletion of stirring, the resulting solution is used as a 1 mol/kgLi_(6.2)La₃Zr_(1.2)Sb_(0.4)Ta_(0.4)O₁₂ precursor (+LDS at aconcentration 10 times the CMC) solution.

COMPARATIVE EXAMPLE 1

The electrolyte precursor solution of Comparative Example 1 is anelectrolyte precursor solution in which the metallic compoundconstituting the crystalline first electrolyte portion 21 is representedby Li_(6.7)La₃Zr_(1.7)Nb_(0.3)O₁₂ (LLZrNbO) and contains LDS as ananionic surfactant at a concentration 4 times the critical micelleconcentration (CMC). That is, the concentration of LDS in thiselectrolyte precursor solution is decreased compared with that ofExample 1. Hereinafter, the preparation of metallic compound solutionsto be used and the preparation of the electrolyte precursor solutionwill be described.

With respect to a lithium source (lithium nitrate), a lanthanum source(lanthanum nitrate hexahydrate), a zirconium source (zirconiumtetrabutoxide), and a niobium source (niobium pentaethoxide), 1 mol/kgsolutions are prepared, respectively, in the same manner as in Example1.

Preparation of 12 mmol/kg Anionic Surfactant Solution (4 Times CMC)

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 0.0327 g of LDS as an anionic surfactant and 9.9673 g of ethanol asa solvent are weighed, and the bottle is placed on a hot plate with astirrer function at a stirrer rotation speed of 300 rpm with an adjustedtemperature of 165° C. Heating and stirring are performed for 30 minutesuntil LDS is completely dissolved. Thereafter, the resulting solution isgradually cooled to room temperature and used as a 12 mmol/kgLDS/ethanol solution.

Preparation of LLZrNbO Precursor Solution

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 8.0400 g of the 1 mol/kg lithium nitrate/2-n-butoxyethanolsolution, 3.0000 g of the 1 mol/kg lanthanum nitratehexahydrate/2-n-butoxyethanol solution, 1.7000 g of the 1 mol/kgzirconium tetrabutoxide/2-n-butoxyethanol solution, 0.3000 g of the 1mol/kg niobium pentaethoxide/2-n-butoxyethanol solution, and 1.0000 g ofthe 12 mmol/kg LDS/ethanol solution are weighed, and the bottle isplaced on a stirrer at a stirrer rotation speed of 300 rpm. Stirring isperformed for 10 minutes until the mixture is completely mixed. Aftercompletion of stirring, the resulting solution is used as a 1 mol/kgLi_(6.7)La₃Zr_(1.7)Nb_(0.3)O₁₂ precursor (+LDS at a concentration 4times the CMC) solution.

COMPARATIVE EXAMPLE 2

The electrolyte precursor solution of Comparative Example 2 is anelectrolyte precursor solution in which the metallic compoundconstituting the crystalline first electrolyte portion 21 is representedby Li_(6.2)La₃Zr_(1.2)Sb_(0.4)Ta_(0.4)O₁₂ (LLZrSbTaO) and contains LDSas an anionic surfactant at a concentration 4 times the critical micelleconcentration (CMC). That is, the concentration of LDS in thiselectrolyte precursor solution is decreased compared with that ofExample 3. Hereinafter, the preparation of metallic compound solutionsto be used and the preparation of the electrolyte precursor solutionwill be described.

With respect to a lithium source (lithium nitrate), a lanthanum source(lanthanum nitrate hexahydrate), and a zirconium source (zirconiumtetrabutoxide), 1 mol/kg solutions are prepared, respectively, in thesame manner as in Example 1, and with respect to an antimony source(antimony triethoxide) and a tantalum source (tantalum pentaethoxide), 1mol/kg solutions are prepared, respectively, in the same manner as inExample 3. As a 12 mmol/kg LDS/ethanol solution, the solution preparedin Comparative Example 1 is used.

Preparation of LLZrSbTaO Precursor Solution

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 7.4400 g of the 1 mol/kg lithium nitrate/2-n-butoxyethanolsolution, 3.0000 g of the 1 mol/kg lanthanum nitratehexahydrate/2-n-butoxyethanol solution, 1.2000 g of the 1 mol/kgzirconium tetrabutoxide/2-n-butoxyethanol solution, 0.4000 g of the 1mol/kg antimony triethoxide/2-n-butoxyethanol solution, 0.4000 g of the1 mol/kg tantalum pentaethoxide/2-n-butoxyethanol solution, and 1.0000 gof the 12 mmol/kg LDS/ethanol solution are weighed, and the bottle isplaced on a stirrer at a stirrer rotation speed of 300 rpm. Stirring isperformed for 10 minutes until the mixture is completely mixed. Aftercompletion of stirring, the resulting solution is used as a 1 mol/kgLi_(6.2)La₃Zr_(1.2)Sb_(0.4)Ta_(0.4)O₁₂ precursor (+LDS at aconcentration 4 times the CMC) solution.

COMPARATIVE EXAMPLE 3

The electrolyte precursor solution of Comparative Example 3 does notcontain an anionic surfactant compared with the electrolyte precursorsolution of Example 1. With respect to a lithium source (lithiumnitrate), a lanthanum source (lanthanum nitrate hexahydrate), azirconium source (zirconium tetrabutoxide), and a niobium source(niobium pentaethoxide), 1 mol/kg solutions are prepared, respectively,in the same manner as in Example 1.

Preparation of LLZrNbO Precursor Solution

In a 20-mL reagent bottle made of Pyrex (trademark) containing a stirrerbar, 8.0400 g of the 1 mol/kg lithium nitrate/2-n-butoxyethanolsolution, 3.0000 g of the 1 mol/kg lanthanum nitratehexahydrate/2-n-butoxyethanol solution, 1.7000 g of the 1 mol/kgzirconium tetrabutoxide/2-n-butoxyethanol solution, and 0.3000 g of the1 mol/kg niobium pentaethoxide/2-n-butoxyethanol solution are weighed,and the bottle is placed on a stirrer at a stirrer rotation speed of 300rpm. Stirring is performed for 10 minutes until the mixture iscompletely mixed. After completion of stirring, the resulting solutionis used as a 1 mol/kg Li_(6.7)La₃Zr_(1.7)Nb_(0.3)O₁₂ precursor solution.

In each of the electrolyte precursor solutions of Examples 1 to 3 andComparative Examples 1 to 3, the feed amount of the lithiumnitrate/2-n-butoxyethanol solution as the lithium source is set to 1.2times the theoretical composition ratio in consideration of scatteringas Li₂CO₃ in the air during firing. Further, as the zirconium source, an80 mass % butanol solution of zirconium (tetra)butoxide is used, andtherefore, the amount thereof is set to 1.25 times (1/0.8) thetheoretical composition ratio when preparing the electrolyte precursorsolutions.

Production of Electrode Assembly

By using each of the electrolyte precursor solutions of Examples 1 to 3and Comparative Examples 1 to 3, electrode assemblies were producedbased on the method for producing an electrode assembly of theabove-mentioned first embodiment. Specifically, first, by using LCOparticles having an average particle diameter D50 of 5 μm, an activematerial portion 11 in which the contour size is ϕ10 mm, the thicknessis 150 μm, and the bulk density porosity is about 50% was prepared.

Subsequently, the active material portion 11 was placed on a hot plate85 through a substrate 84, and 20 μL of the electrolyte precursorsolution of Example 1 was dropped thereon, thereby impregnating theporous active material portion 11 with the solution by utilizingcapillary phenomenon (see FIG. 7). In the case where the electrolyteprecursor solution remained on the surface of the active materialportion 11, the solution was wiped off with Kimwipes wipers S-200(trademark, manufactured by Nippon Paper Crecia Co., Ltd.). Then, thetemperature of the hot plate 85 was set to 87° C., and after thetemperature reached 87° C., the solvent was dried for 15 minutes.Subsequently, the temperature of the hot plate 85 was set to 360° C.,and after the temperature reached 360° C., the hydrocarbons contained inthe electrolyte precursor solution were burned and decomposed for 10minutes. Further, the temperature of the hot plate 85 was set to 540°C., and after the temperature reached 540° C., calcination was performedfor 10 minutes. Thereafter, the resulting calcined body was graduallycooled to 50° C. or lower.

After the above-mentioned procedure was performed 10 times, the mass ofthe obtained calcined body was measured. Thereafter, the calcined bodywas fired at 900° C. for 8 hours using an electric muffle furnace,whereby a main fired body 10 p was obtained. Then, the mass of the mainfired body 10 p was measured.

The bulk density porosity of the main fired body 10 p was determinedbased on the result of measurement of the mass, and a third electrolyte23 p in the form of a powder composed of LCBO was weighed according tothe bulk density porosity. The main fired body 10 p was placed in a pot91, and the weighed third electrolyte 23 p was placed on the main firedbody 10 p and heated in an atmosphere containing carbon dioxide gas,thereby melting the third electrolyte 23 p (see FIG. 9). The main firedbody 10 p was impregnated with the resulting melt 23 m, followed bycooling, whereby an electrode assembly of Example 1 in which the voidsof the active material portion 11 were filled with the electrolyte 20including a crystalline first electrolyte portion 21, an amorphoussecond electrolyte portion 22, and an amorphous third electrolyteportion 23 was obtained. In Example 1, the mass of the melted LCBOpowder is about 5 mg.

Electrode assemblies were produced in the same manner as described aboveusing each of the electrolyte precursor solutions of Examples 2 and 3and Comparative Examples 1 to 3.

With respect to the lithium ion conductivities obtained by AC impedancemeasurement of each of the electrode assemblies obtained using theelectrolyte precursor solutions of Examples 1 to 3 and ComparativeExamples 1 to 3, the values of bulk, grain boundary, and total ionconductivities of the electrolyte in each of the electrode assembliesare shown in the following Table 1. In the AC impedance measurement, inorder to completely exclude the electron conduction property in theelectrode assembly and observe only the lithium ion conduction property,a material obtained by depositing LCBO as an electrolyte to a filmthickness of about 2 μm by a sputtering method on both faces of theelectrode assembly (including the active material portion 11, the firstelectrolyte portion 21, and the second electrolyte portion 22) in theform of a pellet, and thereafter, depositing metallic lithium (Li) by asputtering method in the same manner to form an electrode was used as asample of each of the respective Examples and Comparative Examples.

TABLE 1 Ion conductivity (S/cm) Bulk Grain boundary Total Example 1 — —4.0 × 10⁻⁴ Example 2 — — 4.0 × 10⁻⁴ Example 3 — — 5.8 × 10⁻⁴ Comparative6.2 × 10⁻⁴ 2.2 × 10⁻⁴ 1.6 × 10⁻⁴ Example 1 Comparative — — 2.0 × 10⁻⁴Example 2 Comparative 5.0 × 10⁻⁴ 1.0 × 10⁻⁴ 8.3 × 10⁻⁵ Example 3

As shown in Table 1, in Comparative Example 1 in which the concentrationof the anionic surfactant (LDS) was 4 times the critical micelleconcentration (CMC) and Comparative Example 3 in which LDS was notadded, a grain boundary resistance existed between the active materialportion 11 and the electrolyte 20, and therefore, bulk and grainboundary ion conductivities were obtained in both cases. It isconsidered that the reason why bulk and grain boundary ionconductivities were not obtained in Comparative Example 2 in which theconcentration of LDS was 4 times the CMC is because LLZrSbTaO as theelectrolyte includes the crystalline first electrolyte portion 21 andthe amorphous second electrolyte portion 22 and behaves as if the grainboundary between the crystalline material and the amorphous materialdisappears. In Comparative Examples 1 to 3, the total ion conductivityof Comparative Example 3 in which LDS was not added is 8.3×10⁻⁵ [S/cm],which is the lowest.

On the other hand, in each of Examples 1 to 3 in which LDS was added ata concentration 5 times or more the CMC, bulk and grain boundary ionconductivities were not obtained, and a higher total ion conductivitythan in Comparative Examples 1 to 3 was obtained. This is considered tobe because since LDS is contained in the electrolyte precursor solutionat a concentration 5 times or more the CMC, lithium sulfate derived fromLDS exists between the active material portion 11 and the electrolyte,and the grain boundary resistance becomes smaller even if it is comparedwith that of Comparative Example 2.

Subsequently, lithium batteries using the electrode assemblies ofExamples 1 to 3 and Comparative Examples 1 to 3 were produced based onthe method for producing a lithium battery of the above-mentioned firstembodiment, and the results of evaluation of the battery characteristicthereof are shown in the following Table 2. In the evaluation of thebattery characteristic, charge and discharge were performed at 100 μA(0.2 C), and a case where the discharge amount with respect to theinitial charge amount was 90% or more, and also the 10th dischargeamount with respect to the initial discharge amount was maintained at90% was evaluated as “A (suitable)”, and the other cases were evaluatedas “B (unsuitable)”.

TABLE 2 Concentration Crystalline Amorphous of LDS 1st 10th Evaluationfirst third (magnification charge and charge and of battery electrolyteelectrolyte to CMC) discharge discharge characteristic Example 1 LLZrNbOLCBO 5 times 500 μA 500 μA A 450 μA 405 μA Example 2 LLZrNbO LCBO 15times  500 μA 500 μA A 450 μA 405 μA Example 3 LLZrSbTaO LCBO 10 times 500 μA 500 μA A 455 μA 414 μA Comparative LLZrNbO LCBO 4 times 500 μA500 μA B Example 1 400 μA 300 μA Comparative LLZrSbTaO LCBO 4 times 500μA 500 μA B Example 2 450 μA 351 μA Comparative LLZrNbO LCBO — 500 μA500 μA B Example 3 200 μA 100 μA

As shown in the above Table 2, for each of the lithium batteries usingthe electrode assemblies of Comparative Examples 1 to 3, the batterycharacteristic was evaluated as “B (unsuitable)”. In particular, inComparative Example 3 in which the anionic surfactant (LDS) was notused, the initial discharge amount was 200 μA which was less than halfof the charge amount, and also the 10th discharge amount was half of theinitial discharge amount.

On the other hand, for each of Example 1 in which the concentration ofLDS was 5 times the CMC, Example 2 in which the concentration of LDS was15 times the CMC, and Example 3 in which the concentration of LDS was 10times the CMC, the battery characteristic was evaluated as “A(suitable)”. That is, by using the electrolyte precursor solutioncontaining the anionic surfactant (LDS) at a concentration 5 times ormore and 15 times or less the critical micelle concentration (CMC), thegrain boundary resistance between the active material portion 11 and theelectrolyte 20 is decreased, and the electrode assembly 10 having anexcellent total ion conductivity can be formed. By using this electrodeassembly 10 as a positive electrode, the lithium battery 100 having anexcellent battery characteristic can be provided and produced.

In the electrolyte precursor solution containing the anionic surfactant(LDS) at a concentration exceeding 15 times the critical micelleconcentration (CMC), almost all the LDS is micellized, and therefore,LDS is hardly bonded to the surface of the active material particle 11 aas the anionic surfactant, and the function of the anionic surfactant(LDS) cannot be performed, and thus, a preferred battery characteristicwas not obtained in the same manner as in Comparative Example 3.

Second Embodiment

Electronic Apparatus

Next, an electronic apparatus of this embodiment will be described byshowing a wearable apparatus as an example. FIG. 11 is a perspectiveview showing a structure of a wearable apparatus as an electronicapparatus of a second embodiment.

As shown in FIG. 11, a wearable apparatus 300 as the electronicapparatus of this embodiment is an information apparatus which is wornon, for example, the wrist WR of the human body like a watch and canobtain information associated with the human body, and includes, a band301, a sensor 302, a display portion 303, a processing portion 304, anda battery 305.

The band 301 is in the form of a belt using a resin having flexibilitysuch as, for example, rubber so as to come into close contact with thewrist WR when it is worn, and has a binding portion capable of adjustingthe binding position in an end portion of the band.

The sensor 302 is, for example, an optical sensor, and is placed on theinner face side (the wrist WR side) of the band 301 so as to come intocontact with the wrist WR when it is worn.

The display portion 303 is, for example, a light-receiving type liquidcrystal display device, and is placed on the outer face side (a sideopposite to the inner face on which the sensor 302 is attached) of theband 301 so that a wearer can read the information displayed on thedisplay portion 303.

The processing portion 304 is, for example, an integrated circuit (IC),and is incorporated in the band 301 and is electrically connected to thesensor 302 and the display portion 303. The processing portion 304performs arithmetic processing for measuring the pulse rate, the bloodglucose level, or the like based on the output from the sensor 302. Inaddition, the processing portion 304 controls the display portion 303 soas to display the measurement result or the like.

The battery 305 is incorporated in the band 301 in an attachable anddetachable state as a power supply source which supplies power to thesensor 302, the display portion 303, the processing portion 304, etc. Asthe battery 305, the lithium battery 100 of the above-mentioned firstembodiment is used.

According to the wearable apparatus 300 of this embodiment, by thesensor 302, information or the like associated with the pulse rate orthe blood glucose level of a wearer is electrically detected from thewrist WR, and the pulse rate, the blood glucose level, or the like canbe displayed on the display portion 303 through the arithmeticprocessing or the like by the processing portion 304. On the displayportion 303, not only the measurement result, but also, for example,information indicating the conditions of the human body predicted fromthe measurement result, time, etc. can also be displayed.

Since the lithium battery 100 which is small but has an excellentcharge-discharge characteristic is used as the battery 305, the wearableapparatus 300 which is lightweight and thin and can withstand long-termrepetitive use can be provided. Further, the lithium battery 100 is anall-solid-state secondary battery, and therefore can be repetitivelyused by charging, and also there is no concern about leakage of theelectrolytic solution or the like, and therefore, the wearable apparatus300 which can be used safely over a long period of time can be provided.

In this embodiment, the wearable apparatus 300 of watch type is shown asan example, however, the wearable apparatus 300 may be a wearableapparatus to be worn on, for example, the ankle, head, ear, waist, orthe like.

The electronic apparatus to which the lithium battery 100 is applied asthe power supply source is not limited to the wearable apparatus 300.For example, a head-mounted display, a head-up display, a portabletelephone, a portable information terminal, a notebook personalcomputer, a digital camera, a video camera, a music player, a wirelessheadphone, a gaming machine, and the like can be exemplified. Further,the lithium battery 100 can be applied not only to such consumerapparatuses (apparatuses for general consumers), but also to apparatusesfor industrial use. In addition, the electronic apparatuses according tothe invention may have another function, for example, a datacommunication function, a gaming function, a recording and playbackfunction, a dictionary function, or the like.

The invention is not limited to the above-mentioned embodiments, andappropriate modifications are possible without departing from the gistor idea of the invention readable from the appended claims and theentire specification, and an electrolyte precursor solution thusmodified, a method for producing an electrode assembly using theelectrolyte precursor solution, an electrode assembly, a lithium batteryto which the electrode assembly is applied, and an electronic apparatusto which the lithium battery is applied are also included in thetechnical scope of the invention. Other than the above-mentionedembodiments, various modification examples can be contemplated.Hereinafter, modification examples will be described.

MODIFICATION EXAMPLE 1

The electrode assembly 10 of the above-mentioned first embodiment whichfunctions as a positive electrode includes the active material portion11, the first electrolyte portion 21, the second electrolyte portion 22,and the third electrolyte portion 23, but may not necessarily includethe third electrolyte portion 23.

MODIFICATION EXAMPLE 2

According to the method for producing the lithium battery 100 of theabove-mentioned first embodiment, by adjusting the amount of the melt 23m of the third electrolyte 23 p to be impregnated into the porous mainfired body 10 p, the electrolyte layer 24 can be formed simultaneouslyon the other face 10 a of the electrode assembly 10, and therefore, theelectrode assembly 10 may include the electrolyte layer 24.

MODIFICATION EXAMPLE 3

The configuration of the lithium battery including the electrolyteformed using the electrolyte precursor solution of the above-mentionedfirst embodiment is not limited to the lithium battery 100 in which theelectrode assembly 10 including the electrolyte 20 in the internalcavities is used as a positive electrode. FIG. 12 is a schematiccross-sectional view showing a structure of a lithium battery of amodification example. A lithium battery 200 of a modification exampleshown in FIG. 12 is configured such that a positive electrode 210, anelectrolyte layer 220, and a negative electrode 230 are sandwichedbetween a pair of current collectors 241 and 242.

The electrolyte layer 220 includes at least a crystalline firstelectrolyte portion 221 and an amorphous second electrolyte portion 222,and the first electrolyte portion 221 and the second electrolyte portion222 can be constituted using the solid electrolytes described in theabove-mentioned first embodiment. As a method for forming theelectrolyte layer 220, for example, a sheet is formed using a slurrycontaining a material of the crystalline first electrolyte portion 221by a green sheet method. The slurry contains a binding agent, a poreforming material, and the like other than the material of the firstelectrolyte portion 221. Then, an electrolyte precursor solutioncontaining a metallic compound containing elements constituting thesecond electrolyte portion 222, a solvent capable of dissolving themetallic compound, and an anionic surfactant (for example, LDS)containing a hydrophobic group to which a sulfate group and lithium arebonded is prepared. Impregnation of the calcined sheet with theelectrolyte precursor solution, drying, and firing are repeatedlyperformed, and thereafter, main firing is performed at a temperature of900° C. or higher and lower than 1000° C. By doing this, the electrolytelayer 220 in the form of a sheet in which the amorphous secondelectrolyte portion 222 is filled between the particles of the firstelectrolyte portion 221 in the form of particles, and also lithiumsulfate derived from the anionic surfactant (LDS) exists at theinterface between the first electrolyte portion 221 in the form ofparticles and the second electrolyte portion 222 can be formed. Byexistence of lithium sulfate at the interface between the firstelectrolyte portion 221 in the form of particles and the secondelectrolyte portion 222, the dissociation of lithium ions is enhanced,and therefore, the ion conduction property between the crystalline firstelectrolyte portion 221 and the amorphous second electrolyte portion 222can be improved.

The positive electrode 210 can be formed by stacking the electrolytelayer 220 in the form of a sheet using the same positive electrodeactive material as the active material particles 11 a constituting theactive material portion 11 of the above-mentioned first embodiment by,for example, a green sheet method or the like. The negative electrode230 can also be formed by stacking on the electrolyte layer 220 in theform of a sheet using the negative electrode active materialconstituting the negative electrode 30 of the above-mentioned firstembodiment by, for example, a green sheet method or the like. When thethus formed stacked body in the form of a sheet in which the positiveelectrode 210, the electrolyte layer 220, and the negative electrode 230are stacked is punched into a desired size, a battery cell in the formof a pellet is obtained. For the battery cell, current collectors 241and 242 may be provided.

Also for the current collectors 241 and 242, for example, one type ofmetal (metal simple substance) selected from the metal group consistingof copper (Cu), magnesium (Mg), titanium (Ti), iron (Fe), cobalt (Co),nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), indium (In), gold(Au), platinum (Pt), silver (Ag), and palladium (Pd), an alloy composedof two or more types of metals selected from this metal group, or thelike can be used in the same manner as the current collectors 41 and 42of the above-mentioned first embodiment. Both of the current collectors241 and 242 are not necessarily essential, and a configuration in whicheither one is included may be adopted.

According to such a lithium battery 200 and a method for producing thesame, an excellent ion conductivity can be realized in the electrolytelayer 220, and therefore, the lithium battery 200 which is thin and alsohas an excellent battery characteristic and excellent mass productivitycan be provided or produced.

The entire disclosure of Japanese Patent Application No. 2017-245964,filed Dec. 22, 2017 is expressly incorporated by reference herein.

What is claimed is:
 1. An electrode assembly, comprising: an activematerial portion including a plurality of active material particles andhaving voids inside; and an electrolyte including a crystalline firstelectrolyte portion and an amorphous second electrolyte portion, whereineach of the active material particles, the first electrolyte portion,and the second electrolyte portion contains lithium, the electrolyte iscontained in the voids of the active material portion, and lithiumsulfate is interposed between the surface of the active materialparticles and the electrolyte in the voids, and the first electrolyteportion is a metallic compound represented by the following formula (1)having a garnet-type crystal structure:Li_(7-x)La₃(Zr_(2-x)A_(x))O₁₂  (1) where x satisfies the formula:0.05≤x≤0.6, and A is a metal selected from the group consisting of Nb,Ta, and Sb, and has a crystal radius of 78 pm or more.
 2. The electrodeassembly according to claim 1, wherein the second electrolyte portionincludes metal A.
 3. The electrode assembly according to claim 2,wherein the electrolyte includes an amorphous third electrolyte portionhaving a lower melting point than the first electrolyte portion and thesecond electrolyte portion.
 4. A battery, comprising: the electrodeassembly according to claim 3; a current collector provided so as tocome into contact with the active material particles on one face side ofthe electrode assembly; and a negative electrode provided on the otherface side of the electrode assembly.
 5. The battery according to claim4, wherein the negative electrode is composed of metallic lithium or analloy containing lithium, and a lithium reduction resistant layer isprovided between the other face of the electrode assembly and thenegative electrode.
 6. An electronic apparatus, comprising the batteryaccording to claim 5.